Storage phosphor reader having frame vibration isolation

ABSTRACT

A storage phosphor reader apparatus reads exposed storage phosphors. The reader includes an outer frame assembly including a cassette handling assembly, located on the upper part of the outer frame assembly, for handling vertically oriented cassettes; an inner frame assembly; a first set of vibration isolators for mounting the inner frame assembly on the outer frame assembly, so as to minimize vibrations caused in the outer frame assembly from being transmitted to the inner frame assembly; a storage phosphor scanning assembly; and a second set of vibration isolators for mounting the scanning assembly on the inner frame assembly, so as to minimize vibrations caused in the inner frame assembly frame from being transmitted to the scanning assembly.

FIELD OF THE INVENTION

This invention relates in general to computed radiography imagingsystems and more particularly to a computed radiography storage phosphorreader having improved vibration isolation

BACKGROUND OF THE INVENTION

Computed Radiography (CR) is a well established method of radiographicimaging used in the health care environment. The CR system involvesexposing a storage phosphor contained in a cassette to x-radiation of abody part to produce a latent radiographic image in the storagephosphor. The cassette is presented to a storage phosphor reader wherethe storage phosphor is extracted from the cassette, scanned (read) witha stimulating radiation beam to produce a stimulated radiation imagewhich is converted to an electronic (digital) image which can be stored,displayed, transmitted, or output on film. After the latent image hasbeen scanned, the storage phosphor is erased to remove noise and anyresidual image, and the storage phosphor is replaced in the cassetteready for reuse.

The scanning system typically uses a laser to energize the storagephosphor. Light energy is released from the storage phosphor andcollected using multifaceted, mirrored surfaces, which direct the lightenergy into photodetectors that amplify the signal. The scanningoperation is very sensitive to vibration and impacts, which causerelative movement between the laser and storage phosphor, between thestorage phosphor and the light collector, and vibrations around theconstant velocity drive system, which moves the storage phosphor pastthe scanning laser. Such vibrations can result in undesirable imagedegradation which can affect the diagnostic quality of the radiographicimage. In a known storage phosphor reader, vibration isolation isaccomplished by separating the scanning assembly from the outer frameand from an upper cassette handling assembly by supporting the scanningassembly separately on the floor.

U.S. Pat. No. 4,833,325, issued May 23, 1989, inventors Torii et al.,discloses an image readout apparatus in which stimulable phosphor sheetsare transported along a horizontal path through an image readout system.Vibro-isolating light shield members are interposed between the imagereadout mechanism and a casing, which are individually supported on afloor. Vibro-isolating members are also disposed between a conveyorsystem for delivering a stimulable phosphor sheet and an optical systemfor applying the stimulating light to the stimulable phosphor sheet.

U.S. Pat. No. 4,417,260, issued Nov. 22, 1983, inventors Kawai i.e. al.,discloses an image scanning system in which the optical components forscanning a stimulating light beam across a recording medium and themechanical components for moving the recording medium through the systemin a horizontal direction are all mounted on a single frame which inturn is mounted by way of a vibrating insulator on an outer framestructure.

U.S. Pat. No. 5,440,146, issued Aug. 8, 1995, inventors Steffen et al.,discloses a radiographic image reader wherein a photoreceptive medium istransported horizontally through the reader and an optics module issupported on a support stand by kinematic mounts.

U.S. Pat. No. 6,739,768 B2, issued May 25, 2004, inventors Johnke etal., discloses an apparatus for processing photographic materialhorizontally transported through the apparatus. A housing and aprocessing station are each independently mounted through their ownoscillation-damping connection to a common support base.

None of these patents address the problem of vibration isolation inapparatus in which a storage phosphor is vertically transported througha scanning and erase process.

SUMMARY OF THE INVENTION

According to the present invention, there is provided an apparatusdirected to overcoming these problems.

According to one aspect of the present invention there is provided astorage phosphor reader apparatus comprising: an outer frame assemblyincluding a cassette handling assembly, located on the upper part ofsaid outer frame assembly, for handling vertically oriented cassettes;an inner frame assembly; a first set of vibration isolators for mountingsaid inner frame assembly on said outer frame assembly, so as tominimize vibrations caused in said outer frame assembly from beingtransmitted to said inner frame assembly; a storage phosphor scanningassembly; and a second set of vibration isolators for mounting saidscanning assembly on said inner frame assembly, so as to minimizevibrations caused in said inner frame assembly frame from beingtransmitted to said scanning assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of theinvention will be apparent from the following more particulardescription of the embodiments of the invention, as illustrated in theaccompanying drawings. The elements of the drawings are not necessarilyto scale relative to each other.

FIG. 1 is a perspective view of a storage phosphor reader incorporatingthe present invention.

FIG. 2 is an exploded perspective view of the reader of FIG. 1 showingno cassettes mounted on the cassette handling assembly.

FIGS. 3 and 4 are perspective and exploded perspective views of thereader of FIG. 1 showing cassettes of different sizes loaded onto thecassette handling assembly.

FIG. 5 is a diagrammatic view of an embodiment of the present invention.

FIG. 6 is a diagrammatic, perspective view of the outer frame assemblyof the reader of FIG. 1 showing three low frequency vibration isolatorsfor mounting an inner frame assembly.

FIG. 7 is a diagrammatic perspective view of the inner frame assembly ofthe reader of FIG. 1 showing four higher frequency vibration isolatorsfor mounting the scanning assembly.

FIG. 8 is a diagrammatic perspective view showing the inner frameassembly tipped back looking under to three isolator jackstuds thatsupport the inner frame assembly.

FIG. 9 is a diagrammatic perspective view showing the inner frameassembly mounted on the outer frame assembly.

FIG. 10 is a diagrammatic perspective view of the scanning assemblywhich includes the optical system and scanning system.

FIG. 11 is a diagrammatic, perspective view of the scanning assemblymounted on the inner frame assembly.

FIG. 12 is a diagrammatic, perspective view of the scanning assembly,inner frame assembly, and outer frame assembly assembled together.

FIGS. 13 and 14 are perspective, diagrammatic views showing the FrameLocker mounted to the outer frame assembly and the scanning assembly.

FIGS. 15-19 are diagrammatic views showing details of the Frame Locker.

FIGS. 20-22 are diagrammatic views showing the cam plate in greaterdetail.

FIGS. 23-25 are diagrammatic views showing the Frame Locker in theengaged position.

FIGS. 26-28 are diagrammatic views showing the Frame Locker in thedisengaged position.

FIG. 29 is a diagrammatic view illustrating the cassette storagephosphor movement through the storage phosphor reader.

DETAILED DESCRIPTION OF THE INVENTION

In general, a storage phosphor reader incorporating the presentinvention is provided with three main frame assemblies, an outer frameassembly, an inner frame assembly, and a scanning assembly. A cassettehandling assembly is part of an upper frame assembly supported by theouter frame assembly. The outer frame assembly also supports the innerframe assembly which in turn supports the scanning assembly. Vibrationisolation between the scanning assembly and the outer frame assembly isaccomplished by using two levels of isolation. One level is between theouter frame assembly and the inner frame assembly and the other level isbetween the inner frame assembly and the scanning assembly.

Referring now to the Figures, there is shown an embodiment of thepresent invention. As shown in FIGS. 1-4, storage phosphor reader 10includes a housing 12 having a cassette handling assembly 14 on theupper part thereof. Cassette handling assembly 14 includes a load side15 having several cassette loading locations 16 and an unload side 17having several cassette unloading locations 18. The cassettes on side 15contain exposed storage phosphors to be read by reader 10, whereas thecassettes on side 17 contain storage phosphors that have been read anderased and are ready for reuse. FIGS. 3 and 4 show cassettes 20 ofdifferent dimensions vertically mounted on the load side 15 of cassettehandling assembly 14. Reader 10 is also provided with a central slot 22at which cassettes 20 are sequentially positioned by assembly 14 forscanning. A start button 24 is provided at the front of reader 10.

FIG. 5 diagrammatically shows an embodiment of the present invention. Asshown, reader 10 includes outer frame assembly 30, an inner frameassembly 32, and a scanning assembly 34. The outer frame assembly 30also supports an upper frame assembly 36 having cassette handlingassembly 14. Outer frame assembly 30 is mounted on wheels 31 for ease ofmovement of reader 10. Inner frame assembly 32 is supported on outerframe assembly 30 by a first set of low frequency vibration isolators38. Scanning assembly 34 is mounted on inner frame assembly 32 by asecond set of higher frequency vibration isolators 40. Scanning assembly34 includes a laser and associated optics, a reciprocating galvo mirrorfor scanning the laser beam, and a storage phosphor positioning systemincluding a very smooth motion lead screw drive with feedback controlsto position a storage phosphor relative to the scanning laser beam. Inan implementation of reader 10, the natural frequency of the scanningassembly 34 mounted on isolators 40 to inner frame assembly 32 isapproximately 12 Hz in the axial direction and approximately 21 Hz inthe radial direction.

FIGS. 6-12 show in greater detail the present invention. FIG. 6 showsouter frame assembly 30 as a generally rectangular structure havingthree low frequency vibration isolators 38 mounted on a base plate 50for mounting inner frame assembly 32. Isolators 38 are rubber isolatorswith internally molded compression springs. Isolators 38 are positionedsuch that the entire weight of the inner frame assembly 32, includingthe weight of scanning assembly 34, is equally distributed among them.This equal distribution of weight aids in maintaining an equal amount ofcreep of each isolator.

FIG. 7 shows the inner frame assembly 32 with four vibration isolators40 for mounting scanning assembly 34. FIG. 11 shows inner frame assembly32 mounting scanning assembly 34, computer 60, world wide power supply62, UPS battery backup 64, cooling fans, an electrical box 66 containingall the circuit boards. In the implementation of reader 10, the naturalfrequency of the complete inner frame assembly is approximately 5 Hz inthe axial direction and approximately 3 Hz in the radial direction. Thelow natural frequency of the inner frame assembly 32 isolates thescanning assembly 34 from external impacts against outer frame assembly30 and cassette handling impacts from the upper frame. These impacts arecontained within the outer frame assembly 30 so it can be moved forservice very easily without the need to realign the scanning assembly 34to the cassette handling assembly 14.

FIG. 8 shows inner frame assembly 32 tipped back looking under to seethree jack studs 70 that support inner frame assembly 32 on outer frameassembly 30 by screwing into isolators 38. Jack studs 70 are used duringalignment of reader 10 to “dial out” isolator height, isolator stiffnessand frame tolerances.

FIG. 9 shows inner frame assembly 32 mounted on outer frame assembly 30by isolators 38. Isolators 40 are shown for mounting scanning assembly34. FIG. 10 shows scanning assembly 34 alone and FIG. 11 shows scanningassembly 34 mounted on inner frame assembly 32 by isolators 40. FIG. 12shows scanning assembly 34, inner frame assembly 32, and outer frameassembly 30 assembled together.

According to the invention, the design intent is to drive the naturalfrequency of the inner frame assembly 32 as low as possible in order toprovide lower transmissibility of external vibration and impacts. Todrive the Natural Frequency down required an isolator with a high loadcapability and low stiffness. In the implementation of reader 10, theweight of the inner frame assembly 32 was increased as much as possibleby mounting the world wide power supply, UPS battery backup, eraseassembly, computer and electrical box on the inner frame assembly 32.This helped increase the weight of the assembly to 500 pounds. Thepurpose of the second layer of isolation is to isolate higherfrequencies between the inner frame assembly 32 and the scanningassembly 34. These frequencies were on the order of 50 Hz and higher andcame from internal components, such as fans and other electricaldevices. As shown and described above, two layers of vibration isolationare used to isolate the scanning system from impacts and vibration. Thesource of these impacts were both external (customer induced) as well asinternal (component vibration). Some external impacts include loadingcassettes onto the reader during a phosphor scan, dropping a stack ofcassettes to be loaded onto the reader work surface, removing cassettesfrom the unload side during phosphor scan, bumping the front or sidesduring phosphor scan, and using the reader controls during phosphorscan. The low frequency vibration isolation was designed to provide thenecessary isolation from primarily external impacts and the second layerof vibration isolation was used to provide isolation from primarilyinternally generated sources.

One difficulty with employing vibration isolators in a scanning deviceis that there is the potential of adding a great deal of positionalvariation between critical subassemblies. This variation isunpredictable due to varying amounts of isolator creep, machinelevelness, and frame twist. A function of the cassette handling assembly14 is to transfer a cassette from the cassette handling assembly to anelevator which moves the cassette vertically to the scanning assembly34. This system interface requires repeatable cassette positioning inorder for transfer to occur reliably.

According to a feature of the present invention, a “Frame Locker” (FL)mechanism dynamically locks the scanning assembly 34 to the outer frameassembly 30 during cassette transfer. As shown in FIGS. 13 and 14, FL100 includes a cam follower assembly 101 including rotating cam followermount 102 and four cam followers 104 mounted on the scan assembly 34 anda locating cam plate 106 mounted on outer frame assembly 30. During theassembly of reader 10, the cassette elevator (not shown) is adjusted tothe cassette handling assembly 14. While the adjusted position istemporarily frozen with assembly tooling, the outer frame assembly camplate 106 is positioned over the scan assembly cam follower assembly101. The outer frame assembly cam plate 106 is then rigidly fixed toouter frame assembly 30 and the assembly tooling is removed.

FIGS. 15-19 show FL 100 in greater detail. FL 100 includes an encoderdisc 108 which has four slots 110 used to identify state or position.Encoder disc 108 and cam follower mount 102 are supported on pivot shaft112 having retaining ring 114. Shaft 112 is rotatably supported bybearing and shaft housing 116 mounted on FL mount frame 118. DC motor120 is connected to shaft 112 via timing belt 122 and pulleys 124 and126. Through beam optical sensors 128 and 130 control the FL camfollower positions. Wire tie and base 132 is also provided.

FIGS. 20-22 show the cam plate 106 in greater detail. Cam plate 106 ismounted on frame mount plate 134. Cam plate 106 has four circularregions 136 used to lock the frame assemblies. Cam plate 106 has foursquare regions 138 for clearance when the FL 100 is disengaged.

FIGS. 23-25 show FL 100 in the engaged position. Motor 120 has rotatedcam follower mount 102 to a position at which cam followers 104 arealigned with the circular regions 136 of cam plate 106. An encoder slot110 is located at the engagement position 140 at engage sensor 130.

FIGS. 26-28 show DFL 100 in the disengaged position. Motor 120 hasrotated cam follower mount 102 by 45 degrees to a position at which camfollowers 104 are in the square regions 138 of cam plate 106. Camfollowers 104 have ample clearance within cam plate 106 so that thescanning assembly is vibrationally isolated from the outer frameassembly during the scanning process. An encoder slot 110 is located atthe disengagement position 142 at disengage sensor 128.

The geometric mounting locations of the vibration isolators and FL 100create a system which “hinges” about the isolator positions. Whenactuated, DFL 100 can relocate the frame assemblies in X, theta X, Y,and theta Y, directions to nearly the original fixtured positions.Directional stiffness of the isolators insures that theta Z ismaintained. FL 100 does not control the Z position. The cassettetransfer interface is insensitive to Z variations.

The circular cam profile combined with corner lead-ins and the camfollowers creates a highly efficient locating device. This is contraryto a typical locating device such as a pin in hole arrangement.

FIG. 29 is a diagrammatic view useful in explaining the presentinvention. As shown, after cassettes have been loaded onto assembly 14and the start button 24 actuated, sensors (not shown) detect thepresence of cassettes. When cassette presence sensor 220 detects acassette 20 in the position next to slot 22, a barcode label on thecassette is read by barcode reader 222 which allows the cassetteelevator mechanism 224 to be put into the correct position for theparticular size cassette to be read. In addition, FL 100 is engaged toalign the scanning assembly 34 with the cassette handling assembly 14 onouter frame assembly 30. Cassette handling assembly 14 positions acassette 20 containing an exposed storage phosphor 200 at slot 22 andcassette elevator mechanism 224 engages the cassette 20 and brings itdown to storage phosphor extractor assembly 206. The FL 100 insures theproper alignment for the handoff to the elevator mechanism 224.

Cassette 20 is now registered against a datum structure and clamps 202,204 hold the cassette in position. FL 100 is disengaged, allowingscanning assembly 34 to be isolated through isolators 38 and 40. Storagephosphor 200 is extracted from cassette 20 by extractor assembly 206 andtransported vertically past laser scanner 208 and erase assembly 210 bydrive mechanism 228 at a very constant velocity. After the image hasbeen read and storage phosphor 200 erased, FL 100 is reengaged to bringthe scanning assembly in alignment with cassette handling assembly 14.Drive mechanism 228 causes assembly 206 to reinsert storage phosphor 200into cassette 20 and latch it. Elevator mechanism 224 delivers cassette20 to cassette handling assembly 14 in preparation for processing thenext cassette.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

PARTS LIST

-   10—storage phosphor reader-   12—housing-   14—cassette handling assembly-   15—load side-   16—cassette loading location-   17—unload side-   18—cassette unloading location-   20—cassette-   22—central slot-   24—start button-   30—outer frame assembly-   31—wheels-   32—inner frame assembly-   34—scanning assembly-   36—upper frame assembly-   38—low frequency vibration isolators-   40—higher frequency vibration isolators-   60—computer-   62—world wide power supply-   64—UPS battery backup-   66—electrical box-   70—jack stud-   100—DFL-   101—cam follower assembly-   102—cam follower mount-   104—cam follower-   106—cam plate-   108—encoder disc-   110—slot-   112—pivot shaft-   114—retaining ring-   116—bearing and shaft housing-   118—DFL mount frame-   120—DC motor-   122—timing belt-   124, 126—pulley-   128, 130—through beam optical sensor-   132—wire tie and base-   134—frame mount plate-   136—circular regions-   138—square regions-   140—engagement position-   142—disengagement position-   200—storage phosphor-   202, 204—clamps-   206—extractor mechanism-   208—laser scanner-   210—erase assembly-   220—cassette presence sensor-   222—barcode reader-   224—cassette elevator mechanism-   228—drive mechanism

1. A storage phosphor reader apparatus, comprising: an outer frameassembly including a cassette handling assembly, located on the upperpart of the outer frame assembly, for handling vertically orientedcassettes; an inner frame assembly; a first set of vibration isolatorsfor mounting the inner frame assembly on the outer frame assembly, so asto minimize vibrations caused in the outer frame assembly from beingtransmitted to the inner frame assembly; a storage phosphor scanningassembly; and a second set of vibration isolators for mounting thescanning assembly on the inner frame assembly, so as to minimizevibrations caused in the inner frame assembly frame from beingtransmitted to the scanning assembly.
 2. The apparatus of claim 1wherein the first set of vibration isolators are so located that theweight of the inner frame assembly is evenly distributed between thefirst set of vibration isolators.
 3. The apparatus of claim 1 whereinthe first set of vibration isolators are rubber isolators withinternally molded compression springs.
 4. The apparatus of claim 1wherein the inner frame assembly includes adjustable jack studs thatsupport the inner frame assembly by screwing into the first set ofvibration isolators.
 5. The apparatus of claim 1 wherein the weight ofthe inner frame assembly is increased by mounting components of thereader on the inner frame assembly.
 6. The apparatus of claim 5 whereinthe reader components include a world wide power supply, UPS batterybackup, computer, erase assembly, and electrical box.
 7. The apparatusof claim 1 wherein the first set of isolators have a high loadcapability and low stiffness.